January saw about 1.15 million sign-ups through federal and state insurance exchanges under Affordable Care Act, often known as Obamacare, four months into the six-month enrolment period, Xinhua reported.
The latest enrolment data showed that about 3.3 million Americans have signed up for private insurance plans under Obamacare from last Oct 1 through Feb 1.
The January data has shown a "healthy growth" in enrolment in the Obamacare exchanges, said Health and Human Services Secretary Kathleen Sebelius.
Officials said the latest figures also proved a growing momentum for the Obamacare. The federal-run on-line exchange has gone through a rocky start since its debut last October. The enrolment figures began to rebound since last December after the administration worked around the clock to fix the glitches-plagued website.
However, the latest figure still fell short of its goal, six weeks before the enrolment period ends. The Obama administration initially aimed to enrol seven million people by the end of March. The Congressional Budget Office has lowered its forecast to six million as a result of the website glitches.